Among "natural" refrigerants, R717
holds one of the first places as an alternative to R22 and R502.
Production of ammonia all over the world reaches 120 million tons,
and only small portion of it (up to 5%) is used in the refrigeration
equipment.

Ammonia does not deplete ozone layer (ODP = 0) and does not
directly contribute to increase of greenhouse effect (GWP = 0). Gas
with sharp rank smell harmful for the human body. Tolerance
concentration in the air is 0,02 mg/dm3, which
corresponds to its inclusion volume fraction 0,0028%. In combination
with the air at volume fraction 16...26,8% and availability of the
open fire ammonia is explosive. Ignition temperature with air is 651 oС.

Ammonia vapors are lighter that the air, it is well soluble in
water (one unit of water can resolve 700 units of ammonia which
excludes moisture freezing in the system). Ammonia hardly resolves
mineral oils. It does not effect ferrous metals, aluminum and
phosphorous bronze, but at the presence of moisture it destroys
non-ferrous metals (zinc, copper and its alloys). Moisture mass
proportion in ammonia should not exceed 0,2%.

According to thermodynamic qualities, ammonia is one of the best
refrigerants: as to bulk cold-productivity it considerably exceeds
R12, R11, R22 and R502, has higher heat transfer coefficient
which
allows to use pipes of smaller diameter under assigned
cold-productivity in the heat transfer apparatus. Due to ammonia sharp smell, leakage in
the refrigeration system can be easily detected by the personnel.
Due to these very reasons, R717 found its wide use in large
refrigeration facilities. R717 refrigerant has low cost.

One of the disadvantages
of ammonia is higher value of adiabatic
line (1,31) compared to R22 (1,18) and R12 (1,14), which causes
considerable increase of discharge temperature. In connection with
this, they present strict requirements to thermal stability of
refrigeration oils used in combination with ammonia during a long
period of time at operation of a refrigeration facility. Condenser
should have developed heat-transfer area which results in increase
of its steel intensity.

Proportion between temperature and
pressure of saturated vapors of some refrigerants of
CFC, HCFC and HFC groups

Tem-pera-ture,oC

Refrigerant
pressure , 105 Pa

R11

R12

R13

R13B1

R22

R23

R113

R114

R134a

R142b

R500

R502

R503

R717

-120

0,069

0,100

-100

0,331

0,318

0,475

-80

1,094

0,315

0,104

1,144

0,039

0,146

1,560

-60

0,226

2,818

0,908

0,374

3,135

0,163

0,072

0,270

0,487

3,968

0,219

-50

0,391

4,215

1,445

0,643

4,810

0,299

0,135

0,464

0,814

5,898

0,408

-40

0,641

6,070

2,199

1,049

7,090

0,131

0,516

0,240

0,756

1,296

8,448

0,717

-30

0,092

1,004

8,464

3,222

1,635

10,100

0,027

0,226

0,847

0,402

1,179

1,979

11,730

1,195

-20

0,157

1,509

1,480

4,568

2,448

13,990

0,051

0,369

1,330

0,642

1,771

2,910

15,860

1,901

-10

0,257

2,191

5,200

6,292

3,543

18,910

0,089

0,579

2,007

0,983

2,572

4,143

20,970

2,908

0

0,401

3,086

19,730

8,454

4,976

25,050

0,148

0,875

2,928

1,452

3,626

5,731

27,230

4,294

10

0,605

4,233

25,180

11,120

6,807

32,640

0,236

1,278

4,145

2,079

4,981

7,730

34,810

6,150

20

0,833

5,673

31,710

14,350

9,099

41,930

0,362

1,811

5,716

2,896

6,686

10,200

8,574

30

1,254

7,449

18,220

11,290

0,538

2,500

7,701

3,938

8,794

13,190

11,670

40

1,735

9,607

22,830

15,340

0,778

3,372

10,164

5,244

11,360

16,770

15,550

50

2,346

12,190

28,280

19,420

1,094

4,454

13,176

6,856

14,430

21,010

20,330

60

3,111

15,260

34,690

24,270

1,501

5,775

16,813

8,819

18,080

26,010

70

4,052

2,018

7,364

21,162

11,182

80

5,192

2,659

9,254

13,999

90

3,444

11,480

17,329

100

4,390

14,080

110

5,518

17,100

Ammonia has extremely high value of heat of vaporization and, as
a consequence, comparatively small mass consumption of the
circulating refrigerant (13... 15% compared to R22). It is a
profitable quality for large refrigeration facilities but it makes
regulation of ammonia delivery to the evaporator under low power
difficult.

Additional difficulties while refrigeration equipment production
are caused by ammonia high activity towards copper and copper
alloys; that's why, pipelines, heat-exchangers and accessories are
made of steel. Due to ammonia high toxicity and combustibility,
welded connections are thoroughly controlled. Due to high
conductivity of R717, creation of half-hermetic and hermetic
compressors is impeded. At the same time, for industrial
refrigeration facilities with the power more than 20 kWt, ammonia is
the best alternative.

Many heat pumps are operated on ammonia. Thus, in Norway there's
operating a heat pump with the power of 200 kWt. In the system
there's circulating about 30kg of ammonia, there are used
half-hermetic compressor and plate heat-exchange apparatus. Control
system of ammonia leakage and effective ventilation are
provided.

Using of ammonia in small refrigerating machines for commercial
facilities is expected.

Oils used at the moment are not resolved in ammonia; that's why,
it is necessary to insert into the refrigeration machine model oil
eliminators, which increases its cost. Recently there is carried out
intensive research on development of the oil soluble in ammonia and
creation of refrigeration equipment with the "dry" evaporator. Oil
solubility in ammonia excludes formation of the oil skin on
heat-exchange surfaces which increases heat transfer coefficient
from 2700 up to 9100В tons/(m2*К).

Progress achieved recently in development of refrigerating oils
soluble in ammonia R717 can fundamentally change tendencies in
development of refrigerating machine-building.

Carbon dioxide has low critical temperature (31
oС),
comparatively high triple point temperature (-56 oС), big
pressures in triple point (more than 0,5 МPа) and critical pressure
(7,39 МPа). It can serve as an alternative refrigerant. It is
contained in the atmosphere and biosphere of the Earth, has the
following advantages: low price, simple servicing, compatibility
with mineral oils, insulating and structural materials. At the same
time, while using carbon dioxide it is required water cooling of the
refrigerating machine condenser, increases steel intensity of the
refrigerating facility (compared to steel intensity of facilities
operating on haloid-derivative refrigerants). High critical pressure
has also positive aspect connected with low level of compression and
as a consequence, the compressor's effectiveness becomes
considerable. There exist possible perspectives of using carbon
dioxide in low temperature two=spool facilities and air-conditioning
systems in automobiles and trains. It is also suggested to use in
domestic refrigerators and heat pumps.

R728 refrigerant.
Chemical formula N2

Liquid nitrogen is used as cryogenic refrigerating
substance in some countries (England, USA, etc.). Under the
atmosphere pressure , boiling temperature of nitrogen is -196 oС, and specific heat of vaporization is 199 кJoule/kg.
Non-toxic and ecologically clean (ODP = О, GWP = 0) refrigerant.
Cryogenic method of cooling with liquid nitrogen presupposes its
single use. This method is realized in the machineless running
system where actuating agent does not perform closed cyclic
process.

In connection with discovery in Russia of
considerable reserves (about 340 billion m3) of
underground gases with high content of nitrogen, cost of natural
nitrogen becomes lower compared to nitrogen derived using the method
of air liquation and separation, which will allow to apply in
industrial scale machineless method of cooling in the machines for
quick freezing of food products. In order to increase the level of
using low-temperature potential of gasiform nitrogen, specialists
have suggested the system of mobile cold supply.

R290 refrigerant.
Chemical formula
С3Н8 (propane).

Ozone depletion potential ODP = 0, global warming potential GWP = 3. It is
characterized by low cost and it is non-toxic. While using this
refrigerant, there is no problem with selection of structural
materials for the parts of compressor, condenser and evaporator.
Propane is easily resolved in mineral oils. Boiling point under the
atmospheric pressure is -42,1 oС. The advantage of
propane is also low temperature at the exit out of the compressor.
However, propane as a refrigerant has two fundamental disadvantages.
First, it is fire risky; second, size of the compressor should be
bigger than while using of R22 of the assigned cold-productivity in
the refrigeration machine.

In industrial refrigeration facilities, propane has been used for
many years already. During recent years, more and more often it is
suggested to use propane in refrigeration transport facilities.

In Germany in 1994 there were manufactured more than 1000
domestic refrigerators on propane, isobutane and their blends.
Similar refrigerators are being manufactured in China, Brazil,
Argentina, India, Turkey and Chile. According to estimations of
developers of this equipment, refrigerating factor at using of
hydrocarbons is almost the same (+(-)1%), as while operating on R12.
Only small alterations in the compressor design are required. There
are used the same mineral oils, the same insulation, the same
sealing materials, pipes of the same diameter, the procedure of
servicing is almost unchanged. Discharge temperature becomes lower
than while operating on R22 or R502. Propane can be immediately
charged into the system where there was ozone-depleting refrigerant
before. As the research has shown, in this case up to 10% of
cold-productivity is lost if in the system there was R22 before, and
15% is lost, if R502. A number of specialists believe that this
reduction could be also prevented by adding polypropylene to
propane.

In the USA it is prohibited to use hydrocarbons in domestic
refrigerators. American Environment Protection Agency is foreseeing
up to 30 000 fires per year in case of their use.

In New Zealand hydrocarbons are allowed to use in commercial
refrigeration equipment.

While locating commercial refrigeration equipment operating on
propane in public places, it is necessary to follow safety rules. In
case of exceeding of assigned charging norms (more than 2,5 kg of
R290), refrigeration equipment should be installed in a separate,
specially equipped place which increases capital outlays.

Propane is used also in heat pumps. In Lillehammer (Norway) a
heat pump is operating on propane with power of 45 kWt with
half-hermetic compressor and plate heat-exchangers. In the system of
a heat pump propane mass is a little more than 1 kg; equipment is
placed in a separate building. According to specialists' opinion,
control of fire risk is possible.

R600a refrigerant.
Chemical formula С4Н10 (isobutane).

In comparison with R12 and R134a refrigerants, isobutane has
considerable ecological advantages. This natural gas does not
deplete ozone layer (ODP = 0) and does not cause greenhouse effect
(GWP = 0,001). Mass of the refrigerant circulating in the
refrigeration aggregate at butane using, is considerably reduced
(approximately by 30%). Specific mass of isobutane is twice bigger
than specific mass of the air - gaseous R600a is spread along the
ground. Isobutane is easily soluble in mineral oil, it has higher
refrigerating factor that R12 and it reduces energy consumption.
Physical qualities of R600a compared to R12 and R134a refrigerants
are given in the table.

Isobutane is combustible [refrigerant of the 3rd class (It/DIN
8975)], easily inflammable and explosive, but only in combination
with wax at the refrigerant volume fraction 1,3...8,5%. Lower limit
of explosive risk (1,3%) corresponds to 31 gm of R600a on 1
m3 of the air; upper limit (8,5%) - 205 gm of R600a on 1
m3 of the air. Inflammation temperature is 460 oС.

At the moment, Italian and German companies used R600a in
domestic refrigeration equipment. In particular, companies Necci
compressori" and "Zanussi" of the international concern "Electrolux
compressors" manufacture compressors operating on isobutane.
Refrigeration aggregates with R600a are characterized by lower level
of noise due to low pressure in the refrigerant operating
contour.

The use of isobutane in the existing refrigeration equipment is
connected with the necessity of substitution of the compressors with
compressors of bigger productivity because according to specific
volumetric refrigerating effect, R600a considerably exceeds R12
refrigerant (almost twice).

Basic
physical qualities of R6ООа compared to R12 and
R134a

Parameter

R12

R134a

R600a

Normal boiling point (p = 0,1МPа),
oС

-29,8

-26,5

-12

Freezing point, oС

-158

-101,1

-159

Critical temperature,
oС

122

101,15

135

Critical pressure, МPа

4,11

4,06

3,65

Suction pressure at -15
oС, МPа

0,182

0,164

0,089

Solubility in oil

Not
limited

Water solubility in the contour (at
15.5 oС), mas. %

0,005

0,015

0,0057

Ozone depletion potential (ODP)

1

0

0

Refrigerants related to HFCs group

R 125 refrigerant.
Chemical formula СНF2СF3

Related to HFC group, it does not
contain chlorine. Ozone depletion potential ODP = 0, global warming
potential GWP = 860. Boiling point at the atmospheric pressure is
-48,1 oС. The refrigerant is reccomended to use in a
clear type or as a component of alternative blends to substitute
R22, R502 and R12. R125 refrigerant is fire safe. As to energy
performance and heat-transfer coefficient, it plays back to R22 and
R502 refrigerants. Compared to R502, it has more abrupt curve
characterizing dependence of saturated vapors pressure on
temperature, low critical temperature and not high specific
temperature of heat-vapor buildup which causes the necessity of
increase of the compression level. In connection with this,
possibilities of R125 use in the refrigeration equipment using
condensers with air cooling are extremely limited.

At the same time, R125 has lower (compared to R22 and R502)
discharge temperature and high mass flow under low suction
pressures. Piston refrigeration compressors operating on R125 are
characterized by optimal cylinder charging, and as a consequence,
they have big volume efficiency.

R134a refrigerant is non-toxic and does not flare up within the
whole range of operational temperatures. However, in case of air
ingress into the system and compression there can be formed
combustible blends. You shouldn't mix R134a with R12 because there
is formed azeotrope blend of high pressure with mass proportions of
the components 50 and 50%. Saturated vapor pressure of this
refrigerant is a bit higher than that of R12 (correspondingly 1,16
and 1,08 МPа at 45 oС). R134a vapor is decomposed under
the influence of flame with formation of poisonous and irritating
contextures, such as fluorohydrogen.

According to classification ASHRAE, this product is related to
class А1. In middle-temperature equipment (boiling point -7
oС and higher), R134a has operation performance close to
R12.

R134a is characterized by not high discharge temperature (it is
approximately 8...10oС lower than for R12) and not high
values of saturated vapors pressure.

In refrigeration facilities operating under boiling point lower
than -15 oС, energy data of R134a are worse than those of
R12 ( specific volumetric refrigerating effect is 6% lower at -18 oС), and refrigerating factor. In such facilities it is
purposeful to use refrigerants with lower normal boiling point or
compressor with increased time volume circumscribed by pistons.

In middle temperature refrigeration facilities and
air-conditioning systems, refrigerating factor of R134a is equal to
the factor for R12 or higher than that.

In high-temperature refrigeration facilities, specific
cold-productivity when operating on R134a is also a bit higher (6%
more at tо = t0 oС), than that of R12. Ranges
of using R134a refrigerant are shown in Fig., and dependence of
cold-productivity and refrigerating factor on boiling point is shown
further on the figure.

Due to considerable global warming potential GWP, it is
recommended to use R134a in hermetic refrigerating systems.
Contribution of R134a to greenhouse effect is 1300 times as bigger
as that of СО2. Thus, air venting of R134a one filling
from a domestic refrigerator (about 140 gm) corresponds to ejection
of 170 kg of СО2. In Europe about 448 gm of
СО2 is formed at production of 1 kWt/h of power, that is,
this ejection corresponds to production of 350 kWt*h of power.

For operation with R134a refrigerant, only polyester
refrigeration oils characterized by increased hygroscopic property
are recommended.

R134a is widely used all over the world as a main substitute of
R12 fir refrigeration equipment operating within middle-temperature
range. It is used in automobile air-conditioners, domestic
refrigerators, commercial refrigeration middle-temperature
equipment, industrial facilities, air-conditioning systems in
buildings and industrial areas, as well as on refrigeration
transport. The refrigerant can be used also for retrophite of the
equipment operating at lower temperatures. However, in this case, if
the compressor is not substituted, refrigeration system can have
reduced cold-productivity.

R134a is compatible with a number of sealing materials, in
particular, with pads made of such materials as "Buna-N", "Khailalon
48", "Neopren", "Nordel". As the analysis carried out by company "Du
Pont" showed, change of mass and linear swelling of such materials
used in domestic refrigeration equipment as phenoplast and polyamide
chocks, textolite, paronite and polyethylene terephtalate skins, in
combination of SUVA R134a with polyester oil "Castrol SW100" at 100 oС during 2 weeks have been insignificant.

Analysis of foreign publications and the results
of the research of native specialists indicate that substitution of
R12 for R134a, which has high global warming potential GWP, in
refrigeration compressors is connected with solution of a number of
technical tasks basic of which are:

Improvement of volume and energy performance of hermetic
compressors;

Increasing of chemical constancy of enamel wires of the
hermetic compressor electric motor;

Increasing of dehumidifying ability of filter-dehydrators due
to high hygroscopic property of R134a system - synthetic oil.

All this should result in considerable increase of the cost of
refrigeration equipment. At the same time, in water-cooling plants
with screw and centrifugal compressors the use of R134a has certain
perspectives.

R 143a refrigerant.
Chemical formula
CF3-СН3 (trifluoroethane)

R143a has ozone depletion potential ODP = 0 and comparatively
high global warming potential GWP = 1000, non-toxic and fire-safe,
it does not interact with structural and packing materials. Three
hydrogen atoms in R143a molecule contribute to good solubility in
mineral oils. Specific heat of vaporization is 19,88 kJoule/mole at
normal boiling point which is a bit higher than for R125 (18,82
kJoule/mole). Discharge temperature is lower than that of R12, R22
and R502. As energy analysis has showed, energy effectiveness of
two-step cycle with R143a is close to the effectiveness of the cycle
with R502, lower than that of R22, and higher than that of R125.
R143a refrigerant belongs to composition of multi-component
alternative blends suggested for substitution of R12, R22 and
R502.

R 32 refrigerant. Chemical formula
CF2H2 (difluoromethane).

Related to HFC group. R32 has ozone depletion potential ODP
= О and low global warming potential GWP = 220, in comparison with
R125 and R143a. Non-toxic, fire risky. It has high specific heat of
vaporization 20,37 kJoule/mole at normal boiling point and abrupt
dependence of saturated vapors pressure on the temperature and, as a
result, R32 is characterized by high discharge temperature, which is
the highest of all alternative refrigerants, except ammonia. R32 is
soluble in polyester oils.

When used in refrigeration facilities, R32 is characterized by
high cold-productivity and energy effectiveness, but it is slightly
inferior to R22 and R717. High level of R32 compression causes
necessity of considerable alteration in the refrigeration facility
design at retrophite, and as a consequence, it results in increasing
of its metal intensity and cost. Therefore, R32 is recommended to
use mainly as a component of alternative working blend. Due to small
size of R32 molecule compared to molecules of ethane row
refrigerants, R32 selective leakage through looseness in the
refrigerating system is possible, which can change the composition
of multi-component working blend.